Shaun
For my business, there's no set rule for whether or not I do an in-home audit prior to the clean.
My rules of thumb are, if it's a repeat, then there's probably no need, you'll have enough info on your database. If it's a personal recommend and just a small room, you can estimate over the phone and if that is in the ballpark for the customer confirm as a no obligation quotation when you arrive to do the work. Theoretically you may be turned away, but it's never happened to me yet.
Try and schedule the quote/audit when you're working the area, saves time and expense.
If you are working and quoting, you may wish to consider your presentation. Your avatar Shaun, is acceptable for working and quoting, but some techs will work in jeans or coveralls, so will need to think about this aspect.
I will wear indoor shoes for working, but overshoes for quoting (more visible/obvious if the decision maker is not the one to greet you at the door).
I quote all significant sized domestics and all commercials.
I include a 5% premium for carpet quotations, upholstery as required.
Safe and happy quoting

Ken